This invention relates to dunnage devices, particularly dunnage devices used to cushion panel products such as plywood from impact during shipping by railroad car.
Most panel products, particularly plywood, are manufactured in 4 ft. .times. 8 ft. sheets which are typically stacked in tiers for shipping in railroad boxcars of various standard lengths. Plywood tiers are ordinarily 33 in. high and are, in turn, stacked in parcels of three divided by strips of wood or pallets within the railroad car, each such parcel of stacked tiers being approximately 9 ft. high. Such parcels of plywood usually weigh about 9,900 lbs. apiece.
Some railroad boxcars, usually older ones, are 40 ft. 6 in. in interior length and thus accommodate up to ten parcels of plywood tiers therein leaving 6 inches of additional space to be filled by dunnage, ordinarily at the center of the car. A more common size of boxcar is 50 ft. 6 in. in length and thus will accommodate up to 12 parcels of plywood tiers leaving 30 inches of space near the center of the car to be filled by dunnage. Some newer boxcars are being built with an interior length of 52 ft. 6 in. or 52 ft. 8 in. permitting up to 13 such parcels with six or eight inches, respectively, of space to be filled by dunnage. The most common size boxcar, 50 ft. 6 in. in length, is frequently equipped with a load-positioning system which includes a plurality of vertically oriented brace members removably attached interior to the car for changing the effective width of the interior, as disclosed in the present Applicant's U.S. Pat. No. 3,342,142, and one foot thick bulkheads at both ends of the car for strengthening the car ends against damaging impacts from the shifting of goods, as disclosed in the Applicant's U.S. Pat. No. 3,592,142; as a result, the effective inside length of such cars (commonly designated by the trademark "Ply-Pak Equipped") is 48 ft. 6 in. which accommodates up to 12 parcels of plywood tiers leaving six inches of space to be filled by dunnage. Therefore in many cases the space to be filled is six to eight inches wide.
A variety of approaches have been taken by shippers to fill the space between parcels of plywood within boxcars. In most cases rub strips of veneer are placed against the parcels on either side of the void leaving approximately four inches of space to fill. Some shippers simply wedge pieces of wood downwardly between the rub strips from the top of the load thereby rigidly holding the load in position and providing no cushion from the impacts occuring during switching of the railroad cars and transport in general.
Another approach heretofore taken has been to place a pair of vertically-oriented "two-by-fours" (a standard cut of wood having a rectangular cross-section approximately 11/2 in. .times. 3 1/2 in., although these dimensions are subject to changes in lumber industry standards) between the rub strips with their narrowest sides adjacent the rub strips and held upright by a third two-by-four nailed to the tops of the first two. This approach also provides no cushion against impact and furthermore may enable the load to shift violently for a short distance.
More sophisticated approaches have been taken utilizing inflatable air bags such as the air brace disclosed by Langenberg U.S. Pat. No. 3,145,853 which includes a pair of rub strips integral thereto, the dunnage device of Feldkamp U.S. Pat. No. 3,199,689 which discloses a disposable air bag, and the cargo cushion of Marks U.S. Pat. No. 3,426,891 showing an air bag having an exterior fabric cover for protecting the air bag and distributing impact forces. However, none is protected from virtually complete flattening as is often caused by the motion of one-half of a load (weighing approximately 59,000 lbs. for a 12 parcel car) toward the other half during extreme impact conditions. As a result, such air bags are frequently caused to rupture.
Therefore it can be seen that there is a need for a dunnage device particularly suited for shipping panel products, which are extremely dense and thus have considerable energy which must be absorbed during the shifting and bumping associated with the movement of railroad cars, whereby such dunnage device would provide cushioning against normal shock yet be able to withstand extreme impacts without rupture. Also the device should be reasonably inexpensive and minimize the amount of space required for returning it to a collection point for reuse by shippers.